This invention is concerned with improvements in or relating to metatarsal protectors used in footwear, particularly but not exclusively in safety footwear, namely boots and shoes that are worn in locations and for occupations and pastimes where there is danger of impact and/or compression forces being applied to and injuring the feet of the wearer.
Many industries now require that workers wear safety footwear to protect their feet against injury caused, for example, by impacts from above caused by falling objects, or by compression such as may be caused by a vehicle wheel rolling over the foot. Footwear incorporating additional protective structures for the toes and/or metatarsal regions are also desirable in other applications, such as the sports of ice hockey and rock climbing, or when particularly dangerous equipment is being used, such as axes and chain saws.
The safety footwear that currently is available usually includes a toe protector, such as a steel toe box (sometimes called a box toe) providing a protective arch above the toes, through which any impact or compression force applied to its top surface is transmitted around the toes and through the boot or shoe to the ground. Increasingly provision is made to protect the metatarsal region including the five long bones of the instep that extend from the toes to the remainder of the bones of the foot. Many of the prior proposals for metatarsal protection comprise a guard that is fastened to the exterior of the boot or shoe, but increasingly for convenience, and to ensure that it must be worn, the protector is incorporated into the footwear.
The Occupational Health and Safety Association (OHSA) specifies test and performance standards that have been established by American National Standards Inc. (ANSI) which safety enhanced footwear must pass if they are to be certified by them. The Canadian Standards Association (CSA) have adopted equivalent standards. Metatarsal protectors are not required to pass a compression test, since the toe protector will usually provide all of the protection that is required. The test procedure for measuring impact force resistance involves dropping a standard weight on to the metatarsal portion of a specimen boot (size 9D for men and 8 B for women) at a point 8.9 cm (3.5 in) from the outside tip of the 9D boot toe and 8.6 cm (3.375 in) from the outside tip of the 8B boot, the weight being dropped from a height such that it has the required impact force on contact. Three different values of force are used, namely 101.7 Joules (75 foot pounds), 67.8 Joules (50 foot pounds), and 40.7 Joules (35 foot pounds). For certification the minimum clearance inside the boot after the test, as measured by a permanently compressible wax body under the impact point, must be at least 2.5 cm (1.0 in, usually expressed as 32/32 in) for the 9D boot and 2.4 cm (0.94 in, usually expressed as 30/32 in) for the 8B boot. Footwear meeting the corresponding one of these requirements is certified as meeting the standard Mt/75, Mt/50 or Mt/35 respectively.
At this time toe boxes are most usually made of steel, although toe boxes made of plastics materials are becoming available. Similarly, metatarsal protectors are made of both steel or plastics materials, and the plastics materials at present usually employed are for example high density polyethylene (HDPE) or polypropylene (HDPP), ABS and various proprietary nylons, since these are strong and are economical in price. Metatarsal protectors as currently proposed and as in use, of both metal and plastics materials, present a problem to the wearer arising from the fact that inherently they are very rigid, based on the belief to date that such rigidity is necessary for them to pass the test, and particularly to obtain the Mt75 certification. Although the two lower standards are available, in commercial practice most industries are only interested in purchasing footwear which will meet the highest Mt75 standard. Protectors which have resulted from this thinking are of such rigidity and/or thickness that it is difficult to make the boot sufficiently flexible, so as not to hinder walking or kneeling. One solution has been to make the protectors in several pieces that are hinged together, but this does of course considerably increase the cost. Another solution has been to form them with a plurality of longitudinally spaced, transversely extending slots extending inwards from each edge to leave a smaller, more flexible connection along the centre line. Such flexible connections are of course subject to fatigue breakage, but the average working life of a safety boot is relatively short and, even if they do break, hopefully the boot will still be usable.
It is therefore the principal object of the invention to provide a metatarsal protector that can readily be molded from flexible plastics materials and still meet the test requirements for certification as described above.
It is a another object to provide a metatarsal protector molded from flexible plastics material that is able meet the test requirements for certification as described above while being sufficiently flexible that it provides a minimum of hindrance to walking and kneeling.
It is a further object to provide a metatarsal protector molded from flexible plastics material that is able meet the test requirements for certification as described above, while being sufficiently thin that it can be incorporated into footwear without making it unduly bulky, as seen in side elevation.
In accordance with the present invention there is provided a metatarsal protector for footwear to protect the foot of a wearer from an impact force applied to the metatarsal region thereof, each such footwear comprising an upper having outer and inner surfaces and a sole having outer and inner surfaces, the upper and the sole having respective registering metatarsal regions and being joined to one another with their inner surfaces facing one another;
wherein the protector comprises a protector body having first and second opposite faces, the protector body when incorporated into the footwear being interposed between the registering metatarsal regions with its first surface adjacent to the upper inner surface;
wherein the protector body has two longitudinally extending sides and two transversely extending ends, and when so incorporated is of size to conform to and cover the metatarsal region and of saddle shape, the body first surface is transversely convex and longitudinally concave toward the upper inner surface, and the body second surface is transversely concave and longitudinally convex toward the sole inner surface; and
wherein the protector body is molded from flexible, resilient plastics material and at least the central portion thereof has protruding from one surface thereof a plurality of ridged first projections providing a corresponding plurality of open-mouthed first recesses, each of which first recesses is surrounded by a respective first projection or immediately adjacent first projections that are joined together;
the material from which the protector body is molded has an overall hardness as measured by a Durometer A test of from 35 to 60 Shore; and
the width and height dimensions of the first projections and the corresponding dimensions of the first recesses are such that an impact force applied to the footwear metatarsal region at an impact point results in an acceptable minimum clearance inside the footwear during and after the impact.
The protector body may be provided on the other surface thereof not having the first projections protruding therefrom with a plurality of second projections distributed thereover, the distribution of the second projections being such that they each register with a respective first recess. The shapes of the plurality of second projections may be the same as those of the first recesses and the sizes of the plurality of second projections may be not greater than those of the respective registering first recesses, so that they would fit within those recesses if presented thereto.
Preferably the width and height dimensions of the first projections and the corresponding dimensions of the first recesses, and the width and height dimensions of the second projections when provided, are such that an impact force of up to 35 foot pounds, more preferably of up to 50 foot pounds, and even more preferably of up to 75 foot pounds, applied to the footwear metatarsal region at an impact point results in a minimum clearance inside the footwear after the impact, as measured by a permanently compressible wax body under the impact point, of at least 2.5 cm for a 9 D boot and 2.4 cm for an 8 B boot.